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1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 52
Population Ecology

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Overview: Earth’s Fluctuating Populations
•The size of the human population and its
impact are now among Earth’s most significant
problems
–More than 7 billion individuals
•Requires large amount of materials and
space, land to grow our food, places to
dump our waste
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3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•To understand human population growth
–We must consider the general principles of
population ecology
“No population, including human population,
can continue to grow indefinitely”

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Population ecology is the study of populations
in relation to environment
–Including environmental influences on
population density and distribution, age
structure, and variations in population size

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•The fur seal population of St. Paul Island, off the coast
of Alaska
–Is one that has experienced dramatic
fluctuations in size
Figure 52.1

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Concept 52.1: Dynamic biological processes
influence population, density, dispersion, and
demography
•A population
–Is a group of individuals of a single species
living in the same general area
Rely on the same resources, influenced by
similar environmental factors, have
likelihood of interacting with and breeding
with one another, evolve through natural
selection

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Density and Dispersion
–Every population has specific boundaries and
a specific size.
•Density
–Is the number of individuals per unit area or
volume
•Dispersion
–Is the pattern of spacing among individuals
within the boundaries of the population

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Density: A Dynamic Perspective
•Determining the density of natural populations
–Is possible, but difficult to accomplish
•In most cases
–It is impractical or impossible to count all
individuals in a population

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•Density is the result of a dynamic interplay
–Between processes that add individuals to a
population and those that remove individuals from it
Figure 52.2
Births and immigration add
individuals to a population.
Births Immigration
PopuIation
size
Emigration
Deaths
Deaths and emigration
remove individuals from a
population.

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Patterns of Dispersion
•Environmental and social factors
–Influence the spacing of individuals in a
population

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•A clumped dispersion (most common)
–Is one in which individuals aggregate in patches
–May be influenced by resource availability and
behavior
–Plants/fungi/insects/salamanders
–Animals (mating behavior)
–Protection from predators
Figure 52.3a
(a) Clumped. For many animals, such as these wolves, living in
groups increases the effectiveness of hunting, spreads the
work of protecting and caring for young, and helps exclude
other individuals from their territory.

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•A uniform dispersion
–Is one in which individuals are evenly distributed
–May be influenced by social interactions such as
territoriality (defense of bounded physical space
against encroachment by other individuals)
–Plants –secrete chemicals that inhibit germination
Figure 52.3b
(b) Uniform. Birds nesting on small islands, such as these
king penguins on South Georgia Island in the South
Atlantic Ocean, often exhibit uniform spacing, maintained
by aggressive interactions between neighbors.

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•A random dispersion
–Is one in which the position of each individual
is independent of other individuals
Figure 52.3c
(c) Random. Dandelions grow from windblown seeds that
land at random and later germinate.

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Survivorship curves can be classified into three
general types
–Type I, Type II, and Type III
Figure 52.5
I
II
III
50 1000
1
10
100
1,000
Percentage of maximum life span
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15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Survivorship Curves
•A survivorship curve
–Is a graphic way of representing the data in a
life table

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•The survivorship curve for Belding’s ground squirrels
–Shows that the death rate is relatively constant
Figure 52.4
1000
100
10
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0 2 4 6 8 10
Age (years)
Males
Females

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Concept 52.3: The exponential model
describes population growth in an idealized,
unlimited environment
•It is useful to study population growth in an
idealized situation
–In order to understand the capacity of species
for increase and the conditions that may
facilitate this type of growth

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Exponential Growth
•Exponential population growth
–Is population increase under idealized
conditions
•Under these conditions
–The rate of reproduction is at its maximum,
called the intrinsic rate of increase

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•The J-shaped curve of exponential growth
–Is characteristic of some populations that are
rebounding
Figure 52.10
1900 1920 1940 1960 1980
Year
0
2,000
4,000
6,000
8,000
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20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Concept 52.4: The logistic growth model
includes the concept of carrying capacity
•Exponential growth
–Cannot be sustained for long in any population
•A more realistic population model
–Limits growth by incorporating carrying
capacity

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Carrying capacity (K)
–Is the maximum population size the
environment can support

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The Logistic Growth Model
•In the logistic population growth model
–The per capita rate of increase declines as
carrying capacity is reached

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•The logistic model of population growth
–Produces a sigmoid (S-shaped) curve
Figure 52.12
Exponential
growth
Logistic growth
K 1,500

0 5 10 15
0
500
1,000
1,500
2,000
Number of generations
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24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Concept 52.5: Populations are regulated by a
complex interaction of biotic and abiotic
influences

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Population Change and Population Density
•In density-dependent populations
–Birth rates fall and death rates rise with
population density
•In density-independent populations
–Birth rate and death rate do not change with
population density

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Density-Dependent Population Regulation
•Density-dependent birth and death rates
–Are an example of negative feedback that
regulates population growth
–Are affected by many different mechanisms

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Competition for Resources
•In crowded populations, increasing population
density
–Intensifies intraspecific competition for resources
Figure 52.15a,b
100 100
100
0
1,000
10,000
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Seeds planted per m
2
Density of females
0 70102030405060 80
2.8
3.0
3.2
3.4
3.6
3.8
4.0
(a) Plantain. The number of seeds
produced by plantain (Plantago major)
decreases as density increases.
(b) Song sparrow. Clutch size in the song sparrow
on Mandarte Island, British Columbia, decreases
as density increases and food is in short supply.

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Territoriality
•In many vertebrates and some invertebrates
–Territoriality may limit density

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Cheetahs are highly territorial
–Using chemical communication to warn other
cheetahs of their boundaries
Figure 52.16

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Oceanic birds
–Exhibit territoriality in nesting behavior
Figure 52.17

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Health
•Population density
–Can influence the health and survival of
organisms
•In dense populations
–Pathogens can spread more rapidly

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Predation
•As a prey population builds up
–Predators may feed preferentially on that
species

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Toxic Wastes
•The accumulation of toxic wastes
–Can contribute to density-dependent regulation
of population size

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Intrinsic Factors
•For some populations
–Intrinsic (physiological) factors appear to
regulate population size

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Population Change and Population Density
•In density-
independent
Factors
–These are
abiotic factors
mainly climatic
factors and
disturbances
caused by
human activities
•Impacts
mortality
Climatic factors:
•Rainfall
•Drought
•Extreme
temperatute
Anthropogenic
factors:
•Destruction of
habitat
•Land cultivation
•Pesticides

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Population Dynamics
•The study of population dynamics
–Focuses on the complex interactions between
biotic and abiotic factors that cause variation in
population size

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stability and Fluctuation
•Long-term population studies
–Have challenged the hypothesis that populations of large
mammals are relatively stable over time
Figure 52.18
The pattern of population dynamics observed
in this isolated population indicates that various biotic and abiotic
factors can result in dramatic fluctuations over time in a moose
population.
Researchers regularly surveyed the population of
moose on Isle Royale, Michigan, from 1960 to 2003. During that
time, the lake never froze over, and so the moose population was
isolated from the effects of immigration and emigration.
FIELD STUDY
Over 43 years, this population experienced
two significant increases and collapses, as well as several less
severe fluctuations in size.
RESULTS
CONCLUSION
1960 1970 1980 1990 2000
Year
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1,500
2,000
2,500
Steady decline probably
caused largely by wolf
predation
Dramatic collapse caused by severe
winter weather and food shortage,
leading to starvation of more than
75% of the population

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Extreme fluctuations in population size
–Are typically more common in invertebrates
than in large mammals
Figure 52.19
1950 1960 1970 1980
Year
1990
10,000
100,000
730,000
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39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Concept 52.6: Human population growth has
slowed after centuries of exponential increase
•No population can grow indefinitely
–And humans are no exception

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Global Human Population
•The human population
–Increased relatively slowly until about 1650
and then began to grow exponentially
Figure 52.22
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
1000
A.D.
0
The Plague
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41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Though the global population is still growing
–The rate of growth began to slow approximately
40 years ago
Figure 52.23
1950 1975 2000 2025 2050
Year
2003
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42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Global Carrying Capacity
•Just how many humans can the biosphere
support?

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Estimates of Carrying Capacity
•The carrying capacity of Earth for humans is
uncertain

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ecological Footprint
•The ecological footprint concept
–Summarizes the aggregate land and water
area needed to sustain the people of a nation
–Is one measure of how close we are to the
carrying capacity of Earth

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ecological Capacity
•The actual resource base of each country
–US has an ecological footprint of 8.4 ha per
person but has only 6.2 ha per person of
available ecological capacity. Therefore, US is
already above carrying capacity.
–NZ with ecological footprint of 9.8 ha per
person but an available ecological footprint of
14.3 ha per person. Therefore, NZ is below
carrying capacity.

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Ecological footprints for 13 countries
–Show that the countries vary greatly in their footprint
size and their available ecological capacity
Figure 52.27
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14
12
10
8
6
4
2
0
0 2 4 6 8 10121416
New Zealand
Australia
Canada
Sweden
World
China
India
Available ecological
capacity (ha per person)
Spain
UK
Japan
Germany
Netherlands
Norway
USA
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47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•At more than 7 billion people
–The world is already in ecological deficit

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The End